The present invention relates generally to implantable medical devices, and more particularly, to stents, and even more particularly, to bioabsorbable stents. As used herein the term stent refers to any type of expandable frame work, scaffold or implantable prosthesis for providing support to a body lumen.
Stents are used for a variety of medical purposes in the body including in the coronary arteries, the peripheral arteries, arteries of the neck, cerebral arteries, veins, biliary ducts, urethras, ureters, fallopian tubes, bronchial tubes, the trachea, the esophagus and the prostate.
Stents are typically placed or implanted within a bodily vessel, for example, for treating stenoses, strictures or aneurysms therein. They are implanted to reinforce sections of a blood vessel that are collapsing, partially occluded, weakened, or dilated.
Stents are radially expandable and are typically available in self-expanding configuration and mechanically expandable configuration.
Many stents are manufactured with struts having a zig-zag or serpentine configuration which resembles that of a sine wave, and are described as having a plurality of struts interconnected by peaks and troughs, or by curved intersections.
The peaks and troughs, or generally the curved intersections, in a coronary stent or scaffold are the locations that typically experience a high degree of deformation due to crimping and expansion, as well as the greatest periodic strain due to arterial pulsations. These peaks can develop fractures that often start as a crack in the inner peak and propagate outwards.
For bioabsorbable stents or scaffolds, fractures that occur in a couple of months or less after implantation are suspected to result in higher levels of restenosis or stent thrombosis.
Studies have shown that micro-fractures can be observed in some of the higher strain areas of the stent, including many initiating from the inner peak radius of the peaks interconnecting the stent struts. These micro-fractures can further develop into cracks which propagate outward towards the outer portion of the peak or intersection of the stent struts.
Studies have also established that with many bioabsorbable materials, higher strains can result in accelerated material degradation. This can manifest in the form of cracks that can propagate through the width of the strut or peak leading to fracture.
There remains a need in the art for a bioabsorbable stent having improved strain relief and a mechanism for preventing or stopping crack propagation.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the present disclosure is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the present disclosure may be found in the Detailed Description of the Invention.